Lake Byllesby Dam & Reservoir

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The Lake Byllesby Dam is located on the southern edge of Dakota County. The dam is owned by Dakota County with an exempt license to operate from the Federal Energy Regulatory Commission and water levels regulated by the Minnesota Department of Natural Resources.

Dakota County operates the turbines that produce electricity. The energy produced is sold as part of an agreement with Xcel Energy.

In a year, Lake Byllesby Dam generates enough electricity to power about 2,400 homes.

Dam history

The Lake Byllesby Dam was built in 1910 when Henry M. Byllesby Company constructed it across the Cannon River on the border of Dakota and Goodhue counties. Using mostly hand labor, a crew of 500–600 began work in April 1910 and completed the work in just nine months.

The dam was operated by Northern States Power until 1969 when it was sold to Dakota and Goodhue counties. Dakota County became sole owner in 2009.

The dam created the Lake Byllesby Reservoir, a 3.5–mile long, 1,432–acre lake.

The concrete dam is more than 1,100–feet long and more than 60–feet high from its base with nearly 400 feet of spillway. The crest of the spillway is 854 feet above sea level.

The dam is regulated as a high-hazard dam because of it size and proximity to Cannon Falls.

Repairs and safety improvements

Dakota County completed numerous large-scale projects to improve the safety and operations of the Byllesby Dam.

The process started in 2007 with a letter from the Federal Energy Regulatory Commission (FERC) requiring Dakota County to increase the capacity of the Byllesby Dam from 40,000 cubic feet per second (cfs) to 80,800 cfs which is 100 percent of the Probable Maximum Flood, the most severe possible flood calculated by combining information about precipitation, geology and water management strategies.

To meet this requirement, Dakota County upgraded the Byllesby Dam with two new 65-feet wide by 14-feet tall hydraulically operated crest gates to provide flood control. The total project cost $7.5 million, one half was provided by Minnesota Department of Natural Resources Dam Safety Grant Funds.

In 2015-2016, Dakota County completed repairs to the existing dam structure. Improvements included repairing the bedrock, the concrete face of the dam, and existing gate systems at the top of the dam and adding piers and a bridge over the structure.